MOTOR

Abstract

An engine (31) is mounted in a straddle-seat vehicle on a vehicle body frame (10), with a downframe (14) extending downwards from the steering head tube (11). The engine is provided with a cylinder (33) located behind the downframe, a cylinder head (34) provided on an upper surface of the cylinder, an exhaust pipe (61) extending from the cylinder head towards a rear of the vehicle, and an exhaust gas sensor (71) configured to detect a predetermined characteristic in the exhaust gas. The exhaust pipe extends downwards through one side of the downframe, crosses in front of the downframe, and then extends upwards through the other side of the downframe.The exhaust gas sensor is provided on a rear surface side of the exhaust pipe on one side of the down frame and is located on an outside side in relation to the cylinder in a vehicle width direction.

Description

TECHNICAL AREA

[0001] The present invention relates to a motor. GENERAL STATE OF THE ART

[0002] An engine for a straddle-seat vehicle is known in which the exhaust pipe is curved in a U-shape in front of a downward frame (see, for example, patent reference 1). In the engine described in patent reference 1, a cylinder is provided on a crankcase, and a cylinder head is provided on the cylinder. An exhaust port is formed in the front surface of the cylinder head, and the exhaust pipe extends downward from the exhaust port toward the crankcase. In front of the crankcase, the exhaust pipe is curved upward in a U-shape and extends toward the cylinder. The exhaust pipe passes through the side of the cylinder, extends to the rear of the vehicle, and is connected to an exhaust muffler. LIST OF QUOTES PATENT LITERATURE

[0003] Patent literature 1: JP3489242B

[0004] Although an exhaust gas sensor is attached to the exhaust pipe, if the exhaust pipe is bent into a U-shape, as in patent literature 1, it is difficult to assemble the sensor in front of the engine and route its connecting wire. Furthermore, if the sensor's position is determined primarily for ease of assembly, the sensor may be damaged by foreign objects such as flying stones. SUMMARY

[0005] The present invention was made in consideration of the above aspects, and one object of the present invention is to provide a motor which can improve the ease of assembly and the protective performance of an exhaust gas sensor in a model by having the exhaust pipe cross the front of the cylinder.

[0006] An engine according to one aspect of the present invention for solving the problems described above is an engine for a straddle-seat vehicle mounted on a vehicle body frame, wherein a downframe extends downwards from a steering head tube, the engine comprising: a cylinder located behind the downframe; a cylinder head provided on an upper surface of the cylinder; an exhaust pipe extending from the cylinder head towards a rear of the vehicle;and an exhaust gas sensor configured to detect a predetermined feature in exhaust gas, wherein the exhaust pipe extends downwards through one lateral side of the downframe, crosses in front of the downframe, then extends upwards through the other lateral side of the downframe, and wherein the exhaust gas sensor is provided on a rear surface side of the exhaust pipe on one lateral side of the downframe and is located, in a front view, on an outside side with respect to the cylinder in a vehicle width direction.

[0007] According to the engine in the aspect of the present invention, by providing the exhaust gas sensor using the space on the side of the cylinder, the ease of assembly of the exhaust gas sensor is improved, and the exhaust gas sensor's connecting wire is routed without difficulty. Since the exhaust gas sensor is provided on the rear surface of the exhaust pipe, and the exhaust pipe extends from one side to the other side of the downtube under the exhaust gas sensor, the exhaust pipe can protect the exhaust gas sensor from foreign objects, such as flying stones. BRIEF DESCRIPTION OF DRAWINGS Fig. Figure 1 is a left side view of a straddle-seat vehicle according to the present embodiment. Fig. Figure 2 is a right-side view of the circumference of a motor according to the present embodiment; Fig. Figure 3 is a front view of the circumference of the engine according to the present embodiment. Fig. Figure 4 is a front view of the circumference of a first oxygen sensor according to the present embodiment; Fig. Figure 5 is a view from below of the circumference of the motor according to the present embodiment; Fig. Figure 6 is a left side view of the circumference of the first oxygen sensor according to the present embodiment. DESCRIPTION OF EXECUTION FORMS

[0008] An engine according to one aspect of the present invention is mounted on the body frame of a straddle-seat vehicle. A downtube extends downward from a steering head tube of the vehicle body frame, and one cylinder of the engine is positioned behind the downtube. A cylinder head is provided on an upper surface of the cylinder, and an exhaust pipe extends from the cylinder head toward the rear of the vehicle. The exhaust pipe extends downward through one side of the downtube, crosses in front of the downtube, and then extends upward through the other side of the downtube. An exhaust gas sensor is provided in the exhaust pipe to detect a predetermined feature in the exhaust gas.The exhaust gas sensor is mounted on the rear surface of the exhaust pipe on one side of the downtube and, viewed from the front, is located on the outside of the cylinder in a width-of-the-vehicle direction. By utilizing the space on the side of the cylinder, the sensor's ease of assembly is improved, and the sensor's wiring is routed easily. Because the sensor is mounted on the rear surface of the exhaust pipe, and the exhaust pipe extends from one side of the downtube to the other beneath it, the pipe protects the sensor from foreign objects such as flying stones. embodiment

[0009] A straddle-seat vehicle according to the present embodiment is described below with reference to the accompanying drawings. Fig. Figure 1 is a left side view of the straddle-seat vehicle according to the present embodiment. In the following drawings, an arrow Fr indicates the front of the vehicle, an arrow Re indicates the rear of the vehicle, an arrow L indicates the left side of the vehicle, and an arrow R indicates the right side of the vehicle.

[0010] As in Fig. As shown in Figure 1, a straddle-seat vehicle 1 is implemented by mounting various components, such as an engine 31 and an electrical system, onto a vehicle body frame 10. A pair of main frames 12 extends obliquely rearward and downward from a steering head tube 11 of the vehicle body frame 10, and rear sections of the pair of main frames 12 form a pair of body frames 13 that are bent downward. A down-frame 14 extends downward from the steering head tube 11, and a rearward-bent under-loop 15 is connected to a lower section of the down-frame 14. The rear end sections of the pair of under-loops 15 are connected to lower sections of the pair of body frames 13 such that the vehicle body frame 10 is formed in a cradle shape.

[0011] A front fork 21 is steerably mounted on the steering head tube 11 via a steering spindle (not shown). A handle 22 is provided on the upper section of the front fork 21, and a front wheel 23 is rotatably mounted on the lower section of the front fork 21. A fuel tank 24 is positioned above the upper sections of the pair of main frames 12, and the main frames 12 and the fuel tank 24 are covered from the side by a front cover 25. A seat 26 extends rearward from the fuel tank 24, and a seat frame (not shown), which supports the seat 26 from below, is covered from the sides by the rear side covers 27.

[0012] A pivot arm 28 is pivotally mounted on the body frame 13. The pivot arm 28 extends rearward from the body frame 13, and a rear wheel 29 is rotatably mounted on the rear end of the pivot arm 28. The engine 31 is a four-stroke, single-cylinder engine and is suspended in the vehicle body frame 10 by means of a plurality of suspension mounts 16 and 17. A cylinder assembly, in which a cylinder 33, a cylinder head 34, and a cylinder head cover 35 are stacked, is attached to the upper surface of a crankcase 32 of the engine 31. An air cleaner (not shown) is provided rearward from the cylinder head 34.

[0013] A right cooler 41 and a left cooler 42 (in Fig. (1 only the right radiator 41 is shown) are located in front of the cylinder head 34, and the right radiator 41 and the left radiator 42 are attached to the downframe 14. An exhaust pipe 61 extends downwards from the left side of the front surface of the cylinder head 34, and the exhaust pipe 61 runs through the right side of the cylinder 33 and is connected to an exhaust muffler 62 at the rear of the vehicle. A primary catalyst housing 63 is formed in the exhaust pipe 61 in front of the engine 31, and a secondary catalyst housing 64 is formed in the exhaust pipe 61 behind the engine 31. The primary catalyst housing 63 accommodates a primary catalyst 65 (see Fig. 3) and the secondary catalyst housing 64 accommodates a secondary catalyst (not shown).

[0014] Although it is necessary to provide an oxygen sensor in the exhaust pipe 61 upstream of the primary catalyst 65, the ease of assembly and protective performance of the oxygen sensor must be considered. If the oxygen sensor is provided on the rear surface section of the exhaust pipe 61 upstream of the engine 31, the oxygen sensor's protective performance is ensured. However, there is insufficient space between the engine 31 and the exhaust pipe 61, and the ease of assembly of the oxygen sensor is compromised. If the oxygen sensor is provided on the upper surface or similar of the exhaust pipe 61 upstream of the engine 31, the ease of assembly of the oxygen sensor is improved, but a dedicated protective element is required to ensure its protective performance.Therefore, in the present embodiment, the oxygen sensor is provided on the rear surface side of the exhaust pipe 61 using the empty space on the side of the cylinder 33.

[0015] The extensive structures of the engine are described with reference to the Fig. 2 and Fig. 3 described. Fig. Figure 2 is a left side view of the circumference of the motor according to the present embodiment. Fig. Figure 3 is a front view of the circumference of the engine according to the present embodiment.

[0016] As in Fig. As shown in Figure 2, the pair of main frame 12 and down frame 14 are connected to each other via bridge tubes 19 for reinforcement at the upper section of the vehicle body frame 10. Below the bridge tubes 19, the engine 31 is suspended from the vehicle body frame 10 by suspension mounts 16 and 17. A permanent magnet generator cover 36 is provided on the left side surface of the crankcase 32 of the engine 31, and a sprocket cover 37 is provided behind the permanent magnet generator cover 36. A clutch cover 38 (see Figure 2) is also provided. Fig. 3) is provided on the right side surface of the crankcase 32, and a water pump 39 (see Fig. 3) is provided in front of the clutch cover 38.

[0017] The cylinder 33 is provided on the upper surface of the crankcase 32, the cylinder head 34 is provided on the upper surface of the cylinder 33, and the cylinder head cover 35 is provided on the upper surface of the cylinder head 34. The crankcase 32, the cylinder 33, the cylinder head 34, and the cylinder head cover 35 are positioned behind the downframe 14, and the front section of the crankcase 32 is supported on the suspension bracket 16, which is attached to the downframe 14. A first engine guard 75 and a second engine guard 76 are provided inside and on the left side of the underloop 15 beneath the engine 31. The engine 31 is protected from foreign objects, such as flying stones, by the first engine guard 75 and the second engine guard 76.

[0018] As in the Fig. 2 and Fig. As shown in Figure 3, the right radiator 41 and the left radiator 42 are positioned in front of the cylinder head 34 on both sides of the downward frame 14 in the center of the vehicle. The right radiator 41 is larger than the left radiator 42. In the right radiator 41, a right inlet tank 44 is provided on the lower side of a right radiator core 43, and a right outlet tank 45 is provided on the upper side of the right radiator core 43. In the left radiator 42, a left inlet tank 47 is provided on the upper side of a left radiator core 46, and a left outlet tank 48 is provided on the lower side of the left radiator core 46.

[0019] A thermostat cover 51 is provided on the front surface of the engine 31, and the thermostat (not shown) is provided in the thermostat cover 51. The right inlet tank 44 is connected to the thermostat cover 51 via an inlet hose 52. The right outlet tank 45 and the left inlet tank 47 are connected to each other via an intercooler hose 53. The left outlet tank 48 is connected to the water pump 39 via an outlet hose (a radiator hose) 55. The upper section of the thermostat cover 51 is connected to the right outlet tank 45 via an air vent hose (not shown).

[0020] In the right radiator 41, the cooling water flows upwards from the right inlet tank 44 towards the right outlet tank 45. As the cooling water passes through the right radiator core 43, its heat is radiated into the air. The cooling water is then sent from the right outlet tank 45 to the left inlet tank 47 via the inter-radiator hose 53. In the left radiator 42, the cooling water flows downwards from the left inlet tank 47 towards the left outlet tank 48. As the cooling water passes through the left radiator core 46, its heat is radiated into the air. The heat from the cooling water is radiated in two stages by the right radiator 41 and the left radiator 42, thus improving cooling efficiency.

[0021] The cylinder head 34 and the intermediate section of the outlet hose 55 are connected via a bypass hose (not shown). A bypass passage is formed by the bypass hose to bypass the right radiator 41 and the left radiator 42, returning the coolant from the cylinder head 34 (upstream of the thermostat) to the water pump 39. When the coolant temperature is lower than a predetermined temperature, the thermostat closes, and the coolant is returned from the cylinder head 34 to the water pump 39 via the bypass hose. When the coolant temperature is equal to or higher than the predetermined temperature, the thermostat opens, and the coolant flows into the right radiator 41 and the left radiator 42 to cool the engine 31.

[0022] An exhaust opening 67, obliquely facing the left and lower side, is formed in the front surface of the cylinder head 34, and the exhaust pipe 61 is connected to the exhaust opening 67. The exhaust pipe 61 extends downwards from the exhaust opening 67 through the left side of the downframe 14, crosses the front of the downframe 14, and then extends upwards through the right side of the downframe 14. The exhaust pipe 61 is curved in a U-shape using a space in front of the vehicle body such that the radius of curvature of the curved section of the exhaust pipe 61 is large and the exhaust resistance is reduced. The exhaust pipe 61 extends rearwards through the right side of the cylinder 33, and the rear end section of the exhaust pipe 61 is connected to the muffler 62 (see Fig. 1) connected near seat 26.

[0023] The exhaust pipe 61 is formed in a U-shape upstream of the engine 31 by connecting an upstream pipe 68 and the primary catalyst housing 63. The upstream pipe 68 extends obliquely to the left and lower side from the exhaust opening 67, then curves sharply to the right and crosses the front of the down frame 14. The upstream end (the lower end) of the primary catalyst housing 63 is located upstream of the down frame 14, and the primary catalyst housing 63 extends obliquely to the right and upper side from the downstream end of the upstream pipe 68. The primary catalyst 65 is housed in the primary catalyst housing 63, and air pollutants in the exhaust gas are cleaned as the exhaust gas passes through the primary catalyst 65. A downstream pipe 69 (see Fig. 2) extends from the downstream end of the primary catalyst housing 63.

[0024] In the front view, a first oxygen sensor 71 is provided on the rear surface of the upstream pipe 68, and a second oxygen sensor 77 is provided on the left surface of the primary catalyst housing 63. The first oxygen sensor 71 detects the oxygen concentration in the exhaust gas before it passes through the primary catalyst 65, and the second oxygen sensor 77 detects the oxygen concentration in the exhaust gas after it has passed through the primary catalyst 65. The detection result of the first oxygen sensor 71 is used for feedback control of a fuel injection quantity, and the detection result of the second oxygen sensor 77 is used to diagnose catalyst degradation. Lead wires 72 (of which only one is shown) extend from the rear end sections of the first oxygen sensor 71 and the second oxygen sensor 77.

[0025] The layout of the oxygen sensor is determined with reference to the Fig. Sections 4 to 6 are described in detail. Fig. Figure 4 is a front view of the circumference of a first oxygen sensor according to the present embodiment. Fig. Figure 5 is a view from below of the circumference of the motor according to the present embodiment. Fig. Figure 6 is a side view of the circumference of the first oxygen sensor according to the present embodiment. Fig. 4 is the upstream pipe, indicated by a dashed line for practical purposes.

[0026] As in Fig. As shown in Figure 4, the upstream pipe 68 extends obliquely to the left and lower side of the exhaust port 67 of the cylinder head 34, and the first oxygen sensor 71 is provided on the rear surface of the upper section of the upstream pipe 68 on the left lateral side (of one lateral side) of the downframe 14. Since the entire first oxygen sensor 71 overlaps the upstream pipe 68 in the frontal view, and the first oxygen sensor 71 is covered by the upstream pipe 68 from the front, the first oxygen sensor 71 is protected from foreign matter, such as flying stones, from the front. Because the upstream pipe 68 extends under the first oxygen sensor 71 in the width direction of the vehicle, it is less likely that foreign matter spread from below will strike the first oxygen sensor 71.

[0027] In the front view, the first oxygen sensor 71 is located on the outside (on the left side) with respect to cylinder 33 in the vehicle width direction, and the first oxygen sensor 71 overlaps the permanent magnet generator cover 36. A void exists on the side of cylinder 33 and in front of the permanent magnet generator cover 36, and the first oxygen sensor 71 is provided using this void. Sufficient working space is ensured on the side of engine 31 such that the ease of assembly of the first oxygen sensor 71 is improved and the connecting wire 72 of the first oxygen sensor 71 is easily routed. The connecting wire 72 extends upwards through the rear surface of the outlet hose 55 of the left radiator 42.

[0028] A section of the upstream pipe 68 downstream of the first oxygen sensor 71 is curved such that it extends outwards with respect to the first oxygen sensor 71 in the vehicle width direction from the left side of the downframe 14 and then folds back towards the right side of the downframe 14. The outer surface of the permanent magnet generator cover 36 is on the left side with respect to the leftmost position (the outermost position on one side) of the upstream pipe 68, and the outer surface of the left radiator 42 is on the left side with respect to the outer surface of the magnet cover 36.At the moment of tipping over to the left side, the left radiator 42, the permanent magnet generator cover 36 and the upstream pipe 68 impact the ground in front of the first oxygen sensor 71, thus preventing damage to the first oxygen sensor 71.

[0029] The first oxygen sensor 71 is provided in the upstream tube 68 on the left side of the down frame 14, and the primary catalyst 65 is provided in the primary catalyst housing 63 on the right side of the down frame 14. The first oxygen sensor 71 overlaps the down frame 14 in the left side view (see Fig. 6), and the primary catalyst 65 overlaps the down frame 14 in the right side view. Since the space between the primary catalyst 65 and the first oxygen sensor 71 is partitioned by the down frame 14, the hot air flowing from the primary catalyst 65 towards the first oxygen sensor 71 is blocked by the down frame 14. The primary catalyst 65 is positioned on the opposite side of the first oxygen sensor 71 with the down frame 14 interposed, thus improving the degree of freedom in positioning the first oxygen sensor 71.

[0030] As in the Fig. 4 and Fig. As shown in Figure 5, the outlet hose 55 extends from the left radiator 42 rearward toward the right side of the downward frame 14. In the front view, the first oxygen sensor 71 is located below the outlet hose 55, and the outlet hose 55 covers the sensor from above, thus protecting it from foreign objects entering from above. Since the left radiator 42 and the outlet hose 55 are located above the first oxygen sensor 71, the ease of assembly of the sensor is not impaired by the radiator 42 and the outlet hose 55.

[0031] In the bottom view, the first oxygen sensor 71 is positioned in a space surrounded by the upstream pipe 68, the outlet hose 55, and the underloop 15. In this configuration, the upstream pipe 68 is located in front of the first oxygen sensor 71, the outlet hose 55 is located on the left side and rear of the first oxygen sensor 71, and the underloop 15 is located on the right side of the first oxygen sensor 71. Because the outlet hose 55 is located on the left side relative to the first oxygen sensor 71, it will impact the sensor first in the event of a tip-over, thus preventing damage to the first oxygen sensor 71.

[0032] As described above, the plate-shaped first motor guard 75 is attached to the inside of the underloop 15, and the plate-shaped second motor guard 76 is attached to the left side of the underloop 15. The first motor guard 75 extends front to rear such that it covers the crankcase 32 from below, and the second motor guard 76 extends front to rear to cover the permanent magnet generator cover 36 from below. In the view from below, the rear end section of the first oxygen sensor 71 overlaps the second motor guard 76, and the first oxygen sensor 71 is covered from below by the second motor guard 76, thus protecting the first oxygen sensor 71 from foreign objects from below the motor 31.

[0033] As in Fig.As shown in Figure 6, a rearwardly curved base 73 is provided on the rear surface of the upstream tube 68, and the first oxygen sensor 71 is provided on a hump 74 attached to the base 73. The cross-sectional area of ​​the upstream tube 68 is increased by the curvature of the base 73, and the influence of pressure loss due to the protrusion of the distal end of the first oxygen sensor 71 is minimized. Even if the upstream tube 68 has a large number of bends, the detection accuracy of the first oxygen sensor 71 is ensured. Since the hump 74 is not provided directly on the downstream tube 68, it is not necessary to machine the hump shape along the tube shape to reduce pressure loss. The hump 74 is provided on the base 73 in such a way that the hump shape is a simple cylindrical shape, thus reducing costs.

[0034] As described above, the essentially triangular suspension bracket 16 is provided on the downframe 14, and the first oxygen sensor 71 overlaps the suspension bracket 16 in the side view. Since space is provided on the side of the suspension bracket 16 for ease of assembly of the engine 31, the first oxygen sensor 71 is readily provided on the upstream tube 68 of the left side of the suspension bracket 16. Because a large portion of the first oxygen sensor 71 is covered by the suspension bracket 16 from the right side, the first oxygen sensor 71 is protected from foreign matter from the right side of the downframe 14, and the hot air from the primary catalyst 65 towards the first oxygen sensor 71 is blocked by the suspension bracket 16.

[0035] As described above, according to the engine 31 in the present embodiment, the first oxygen sensor 71 is provided using the space on the side of the cylinder 33 in such a way that the ease of assembly of the first oxygen sensor 71 is improved and the connecting wire 72 of the first oxygen sensor 71 is routed without difficulty. Since the first oxygen sensor 71 is provided on the rear surface of the exhaust pipe 61, and the exhaust pipe 61 extends from one side to the other side of the downward frame 14 beneath the first oxygen sensor 71, the exhaust pipe 61 can protect the first oxygen sensor 71 from foreign objects, such as flying stones.

[0036] In the present embodiment, the oxygen sensor is used as an example of an exhaust gas sensor. Alternatively, the exhaust gas sensor can be any sensor capable of detecting the average characteristics of the exhaust gas and can, for example, be an exhaust gas temperature sensor that detects the exhaust gas temperature.

[0037] In the present embodiment, the first and second oxygen sensors, which serve as the exhaust gas sensors, are provided in the exhaust pipe, but it is sufficient that at least one exhaust gas sensor is provided in the exhaust pipe.

[0038] In the present embodiment, the vehicle body frame is provided with an underloop, but the shape of the vehicle body frame is not particularly restricted as long as a lower frame extends downwards from the at least one steering head tube into the vehicle body frame.

[0039] In the present embodiment, a water-cooled engine serves as an example of the engine. Alternatively, the engine can be an air-cooled engine or an oil-cooled engine.

[0040] The engine according to the present embodiment is not limited to use in the straddle-seat vehicle described above and can be used in other types of straddle-seat vehicles. The straddle-seat vehicle is not limited to a general vehicle in which the rider sits astride the seat and includes a scooter-type vehicle in which the rider rides without sitting astride the seat.

[0041] As described above, a first aspect provides an engine (31) for a straddle-seat vehicle (1) mounted on a vehicle body frame (10) in which a downframe (14) extends downward from a steering head tube (11), the engine (31) comprising: a cylinder (33) located behind the downframe; a cylinder head (34) provided on an upper surface of the cylinder; an exhaust pipe (61) extending from the cylinder head towards a rear of the vehicle; and an exhaust gas sensor (a first oxygen sensor 71) configured to detect a predetermined feature in exhaust gas, the exhaust pipe extending downward through one side of the downframe, crossing in front of the downframe, and then extending upward through the other side of the downframe.and wherein the exhaust gas sensor is provided on a rear surface of the exhaust pipe on one side of the downframe and, in a front view, is located on an outside side relative to the cylinder in a vehicle width direction. According to this configuration, providing the exhaust gas sensor using the space on the side of the cylinder improves the ease of assembly of the exhaust gas sensor, and the exhaust gas sensor's lead wire is routed without difficulty. Because the exhaust gas sensor is provided on the rear surface of the exhaust pipe, and the exhaust pipe extends from one side of the downframe to the other side beneath the exhaust gas sensor, the exhaust pipe can protect the exhaust gas sensor from foreign objects, such as flying stones.

[0042] A second aspect relates to the first, whereby a section of the exhaust pipe downstream of the exhaust gas sensor is curved in such a way that it extends outwards towards the sensor in the vehicle's width direction along one side of the downtube frame and then folds back towards the other side. According to this configuration, damage to the exhaust gas sensor can be prevented because, in the event of a rollover, the exhaust pipe strikes the ground in front of the sensor on one side. The shape of the exhaust pipe also protects the sensor from foreign objects.

[0043] A third aspect relates to the first and second aspects, wherein the engine further includes a pair of radiators (a left radiator 42 and a right radiator 41) provided on both lateral sides of the downframe, and wherein a radiator hose (an outlet hose) 55 extends from the radiator (the left radiator 42) on one lateral side of the downframe, and wherein the exhaust gas sensor is located below the radiator hose in the front view. According to this configuration, the ease of assembly of the exhaust gas sensor is not impaired by the radiator and the radiator hose. The exhaust gas sensor is covered from above by the radiator hose, so that the exhaust gas sensor can be protected from foreign objects entering from above.

[0044] A fourth aspect relates to the third aspect, wherein the radiator hose extends from the radiator rearward along one side of the downframe and then extends to the other side of the downframe, and wherein the exhaust gas sensor is provided in a space which, in a view from below, is surrounded by the exhaust pipe and the radiator. According to this configuration, damage to the exhaust gas sensor can be prevented by the radiator hose striking the ground in front of the exhaust gas sensor at the moment of a tip-over on one side.

[0045] A fifth aspect relates to one of the first four aspects, wherein a suspension bracket (16) for the engine is attached to the downframe, and the exhaust gas sensor overlaps the suspension bracket in a side view. Since, according to this configuration, space is provided on the side of the suspension bracket for ease of engine assembly, the exhaust gas sensor is readily provided on the exhaust pipe on one side of the suspension bracket. The exhaust gas sensor is covered by the radiator hose from the side in such a way that it is protected from foreign objects from the other side of the downframe.

[0046] A sixth aspect relates to one of the first five aspects, wherein the engine further includes an engine guard (a second engine guard 76) provided below the engine, and wherein the exhaust gas sensor overlaps the engine guard in a view from below. According to this configuration, the exhaust gas sensor is covered from below by the engine guard in such a way that the exhaust gas sensor can be protected from foreign objects from under the machine.

[0047] A seventh aspect relates to aspects one through six, wherein a rearwardly curved base (73) is provided on a rear surface of the exhaust pipe, and the exhaust gas sensor is mounted on the base. According to this configuration, the cross-sectional area of ​​the exhaust pipe is increased by the curvature of the base, and the influence of pressure loss due to the protrusion of the exhaust gas sensor can be minimized. The detection accuracy of the exhaust gas sensor can be ensured even in exhaust pipes with a large number of curved sections.

[0048] An eighth aspect relates to aspects one through seven, wherein the engine further incorporates a catalyst (a primary catalyst 65) provided in the exhaust pipe on the opposite side of the downframe, and wherein the exhaust gas sensor and the catalyst overlap the downframe in a side view. According to this configuration, the hot air from the catalyst towards the exhaust gas sensor can be blocked by the downframe. The catalyst is provided on the opposite side of the first oxygen sensor with the downframe interposed, thus improving the degree of freedom in providing the exhaust gas sensor.

[0049] Although the present embodiment has been described, part or all of the embodiment and modification described above can be combined to form another embodiment.

[0050] The technology according to the present invention is not limited to the embodiment described above and can be changed, replaced, and modified in various ways without departing from the spirit of the technical concept. The present invention can also be implemented by other methods, provided that the technical concept can be implemented by those methods through technological advancements or other derived techniques. The claims therefore cover all embodiments that may fall within the scope of the technical concept. REFERENCE MARK LIST 1 straddle seat vehicle 10 vehicle body frames 11 Steering head tube 14 Downward frames 16 Suspension bracket 31 Engine 33 cylinders 34 Cylinder head 42 left radiator (cooler) 55 Outlet hose (radiator hose) 61 Exhaust pipe 65 Primary Catalyst (Catalyst) 71 First oxygen sensor (exhaust gas sensor) 72 conductor wire 73 sockets 76 Second engine protection (engine protection)

Claims

[1] Engine (31) for a straddle-seat vehicle mounted on a vehicle body frame (10) wherein a downward frame (14) extends from a steering head tube (11) wherein the engine comprises: a cylinder (33) located behind the downward frame; a cylinder head (34) provided on an upper surface of the cylinder; an exhaust pipe (61) extending from the cylinder head towards the rear of the vehicle; and an exhaust gas sensor (71) configured to detect a predetermined feature in exhaust gas, wherein the exhaust pipe extends downwards through one side of the downframe, crosses in front of the downframe and then extends upwards through the other side of the downframe, and wherein the exhaust gas sensor is provided on a rear surface side of the exhaust pipe on one side of the downward frame and is located on an outside side in a front view with respect to the cylinder in a vehicle width direction. [2] Engine according to claim 1, wherein a section of the exhaust pipe downstream of the exhaust gas sensor is curved such that it extends to an outside in relation to the exhaust gas sensor in the vehicle width direction on one lateral side of the down frame and then folds back to the other lateral side of the down frame. [3] Motor according to claim 1 or 2, comprising: a pair of radiators provided on both lateral sides of the downframe; and a radiator hose extending from the radiator on one lateral side of the downframe, with the exhaust gas sensor extending below the radiator hose in the front view. [4] Motor according to claim 3, wherein the exhaust pipe extends rearward from the radiator on one side of the downframe and then extends to the other side of the downframe, and the exhaust gas sensor is provided in a space which, in a view from below, is surrounded by the exhaust pipe and the radiator hose. [5] Engine according to claim 1 or 2, wherein a suspension bracket for the engine is attached to the downward frame and the exhaust gas sensor overlaps the suspension bracket in a side view. [6] Engine according to claim 1 or 2, further comprising an engine guard configured to protect the engine, which is provided below the engine, wherein the exhaust gas sensor overlaps the engine guard in a view from below. [7] Engine according to claim 1 or 2, wherein a base which curves backwards is provided on a rear surface side of the exhaust pipe and the exhaust gas sensor is provided on the base. [8] Engine according to claim 1 or 2, further comprising a catalyst provided in the exhaust pipe on the other side of the down frame, wherein the exhaust sensor and the catalyst overlap the down frame in a side view.

Images